MB-12468 SSL ctx leaked when connection closed. (mcd data socket)

Ensure we free the ssl_ctx in conn_cleanup

Change-Id: I40d502a9f00b6c408ef9d5fdbe536b0d6437c0fd
Reviewed-on: http://review.couchbase.org/42508
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>